Electro-mechanical transducer for secondary oil recovery and method therefor



Set 1970 E. H. PHILLIPS 3,527,30fi

ELECTRO-MECHANICAL TRANSDUCER FOR SECONDARY OIL RECOVERY AND METHOD THEREFOR Filed Sept. 20, 1968 2 Sheets-Sheet l IINVENTOR. EDWARD H. PHILLIPS Eva/A,

Qwmk W ATTORNEYS p 8, 1970 E. H. PHILLIPS ,300

ELECTRO'MECHANICAL TRANSDUCER FOR SECONDARY OIL RECOVERY AND METHOD THEREFOR Filed Sept. 20, 1968 2 Sheets-Sheet 2 F/G. Z

INVENTOR. EDWAR D H. PHILLIPS BY iM, WELL Mu w W' ATTORNEYS United States Patent 3,527,300 ELECTRO-MECHANICAL TRANSDUCER FOR SECONDARY OIL RECOVERY AND METHOD THEREFOR Edward H. Phillips, Los Altos, Calif., assignor to Electro- Sonic Oil Tools, Inc., a corporation of California Filed Sept. 20, 1968, Ser. No. 761,139 Int. Cl. Ellb 43/25 US. Cl. 166-249 14 Claims ABSTRACT OF THE DISCLOSURE An electro-mechanical transducer for use in secondary recovery in oil wells which, in effect, produces a dipole type radiation field which extends along a single axis perpendicular to the axis of the oil well. This allows the surrounding liner to vibrate in a displacement mode rather than in a circumferential expansion mode, to increase the energy coupling to the surrounding oil-producing formation. In a specific form of the invention, the transducer includes two cylindrical masses, one inserted inside the other, which are coupled by a tubular piezoelectric element driven at an audio or sonic frequency by an external electrical power source.

BACKGROUND OF THE INVENTION The present invention is directed to an electromechanical'transducer for secondary oil recovery and a method therefor and more particularly to a transducer which, because of its vibratory mode, effectively couples mechanical or sonic energy to an oil-producing formation.

Underground oil is dispersed throughout the tiny pore spaces and hairline cracks of rock formations. When a well penetrates the rock, the static pressure head present in the formation drives some of the oil up the well bore. There are four types of natural recovery drives: expansion of gas dissolved in oil; pressure on the oil from expansion of a gas cap above it; force of water on the oil from below or from the edge of the field; and the weight of the oil itself in deeply dipping formations.

Sometimes these natural drives are so strong they not only move oil into the wells, but push it up to the surface. In many fields, however, the natural pressure is just enough to deliver the oil to the well bore, and it must be pumped to the surface.

On the average, nature provides reservoir rock and fluid conditions that allow production of only 25 percent of the oil in a reservoir, leaving 75 percent still dispersed in the rock. Techniques to recover this remaining 75 percent are known as secondary recovery. Secondary recovery broadly includes methods of injecting liquids or gases into oil reservoirs to drive or flush additional oil from them. Injected fluid displaces oil in the reservoir in essence providing a man-made or artificial pressure head. Major types of secondary recovery include gas injection, water injection, steam injection, underground combustion, and miscible drive.

Secondary recovery is especially useful and necessary in shallow viscous type oil fields such as are found in California.

Another secondary recovery technique which has been used in conjunction with the other techniques or by itself in an attempt to remove flow-impeding materials has been vibrations using sonic wave energy. An electro-acoustic or mechanical-acoustic transducer is lowered in the well which radiates sonic waves into the oil-bearing formations surrounding a well to open up blocked passages to thereby increase the flow of petroleum fluid from the formation to the well bore. While advantages of this sound 3,527,300 Patented Sept. 8, 1970 energy technique have been appreciated for many years,

prior attempts to generate useful energy have suffered SUMMARY OF THE INVENTION AND OBJECTS Accordingly, it is a general object of the invention to provide an improved electro-rnechanical transducer and transduction system for effectively coupling energy to a fluid medium, such as an oil-bearing formation.

It is a more specific object of the invention to provide a transducer as above which is effective in secondary oil recovery.

It is another object of the invention to provide an electro-mechanical transducer for use in oil wells which effectively transfers energy through the casing of the oil well to the surrounding oil formation.

It is another object of the invention to provide an improved method for secondary oil recovery with the use of the above transducer.

It is another object of the invention to provide a transducer which includes a vibratory element which is matched to the surrounding medium by a pair of masses which are mechanically coupled thereto.

In accordance with the above objects, there is provided an electro-mechanical transducer for use in an oil well which extends along a predetermined axis. The transducer has a major effective radiating surface providing radiation perpendicular to the predetermined oil well axis, the major force pattern being directed along an axis perpendicular to the oil Well axis.

In a more specific form the transducer itself includes a vibratory element with means for driving the element. A first mass interfaces with a fluid medium such as oil and includes a cavity having a predetermined geometrical axis. A second mass has at least a portion extending into this cavity. Spring means including the vibratory element couple the two masses so that the resulting spring force are represented by vectors substantially perpendicular to the geometrical axis of the first mass.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view partially cut away of an oil well casing with several electro-mechanical transducers embodying the present invention inserted therein.

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1 illustrating the electro-mechanical transducer of the present invention along with lines of force indicating the path of energy transmission into the surrounding formation.

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 1.

FIG. 4 is a cross-sectional view taken substantially along the line 4-4 of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, there is illustrated the lower end portion of an oil well showing a casing 11 having the usual perforations 12 to allow oil to flow in from the surrounding oil-bearing formation indicated at 13. Pump means are associated with the casing whereby the oil can be pumped to the surface. In the example shown, the pump means includes a pump tube 14 which extends downwardly from the surface along the interior of the casing 11. An actuating rod 16 is located in the interior of pump tube 14. The rod is coupled to a pump schematically shown at block 17. The inlet of the pump is shown at 20. Up and down movement of actuating rod 16 causes suction to be created at 20 to allow entry of any available fluid or oil at inlet 20 to be pumped to the surface through tube 14. Pump 17 would normally be contained within the diameter of the pump tube.

Several stacked electro-mec-hanical transducers 18, 19 and 21, rigidly coupled together by intermediate discs 22 to form a unitary assembly, are supported at the bottom of pump tube 14 in proximity to the oil-bearing forma- V tion 13.

It should be appreciated at this point that although a pump assembly 16, 17, 20 has been illustrated, in flowing wells, where there is suflicient natural pressure, the pump is not required. Also, for other applications where pressure is applied, for example, by a water flood method or gas infusion, the pump may not be required.

The construction of each of the electro-mechanical transducers is illustrated in FIG. 2 which is a cross-section of transducer 21. Each transducer is composed of a first cylindrical mass 23 which includes therein an olfcenter cylindrical cavity 24. A second cylindrical mass 26 is inserted in cavity 24 and coupled to the first mass 23 by a spring means which includes piezoelectranducer 27 which is in the form of a cylindrical tube and bolt 28 which provides a compressive force to sandwich the transducer between the masses 23 and 26. The transducer interfaces with the masses at 29 and 30. In certain instances, a compliant material may be provided at the interface to assure a competent mechanical connection between the masses 23 and 26 :and the transducer or vibratory element 27.

Transducer element 27 is driven in a longitudinal mode of vibration by the application of an alternating electrical energy between its outer cylindrical surface 31 and its inner cylindrical surface 32. Alternating electrical energy of sufficient magnitude causes these two surfaces to move alternately towards and away from each other in radial compression and expansion, and by reason of Poissons ratio, the piezoelectric element axially extends and contracts at a frequency corresponding to that of the electrical energy.

Generally, the bolt 28 and element 27 serve in their extension mode as a combined set. Two each sets are used per transducer sections 18, 19 or 21. The spring stiffness is chosen so that the two-mass spring system, which includes the masses 23 and 26, will resonate at the desired frequency. The spring stiffness is determined by the length and diameter of the element 27 and the diameter and material of the bolt 28. The resonant frequency is chosen so that it is resonant with the resonant cavity formed by the oil-filled circumferential gap 50 defined by the outer surface of mass 23 and the inside surface of the well casing 11. The resonant frequency of the transducer is determined by the mean circumference of the gap. The resonant wavelength A, which determines the frequency of operation, equals the circumference. It is, of course, apparent that there will be resonances at harmonic frequencies of the fundamental.

When the transducer is operated at resonance, the masses 23 :and 26 move in opposite directions as indicated by the arrows 23 and 26, FIG. 2. This, in turn, causes the transducer assembly to move back and forth in a direction substantially perpendicular to its longitudinal axis. The energy is transferred through the oil in the cavity, through the casing 11 and into the formation where it radiates outwardly in a dipole pattern as will be more fully explained below.

An electrical conductor is attached to the inside surface of the vibratory element 26 and, as shown at 33,

extends along the cut-out wireway 34 formed in the mass 26.

The electrical coupling of all of the transducer assemblies 18, 19 and 21 is best shown in FIG. 1 where the wire 33 extends up to the connector 35, and thence through the casing 11 to :a power source at the surface. If desired, the conductor may connect on only one side of the interior of the vibratory element 29 as actually illustrated in FIG. 1, with the other side being grounded through the pump tubing.

Each disc 22 is bolted to the adjacent upper end of the adjacent mass 23 by short bolts (not shown). The electromechanical transducers are coupled to one another by longer 'bolts 36 which are threadably received by the disc or member adjacent the lower end of eachmass 23. The mass 23 of each transducer includes circumferentially disposed bolt passages 37 adapted to receive the bolts. The upper end 38 of the bolt passage is recessed to accommodate the bolt head. A disc 22 is disposed at the lower end of the mass 23 and threadably receives the bolt whereby the lower disc 22 can be secured to the transducer. The lower disc is secured to the next mass giving a complete multiple transducer assembly.

In order to provide, in effect, a rigid integral multiple transducer assembly, the disc 22 and mass 23 of each transducer contains raceways 41 and 42 as shown in FIGS. 3 and 4. Inserted in the raceways are balls 44 which are slightly oversized. When the transducers are stacked, compressive stress is brought to bear on the balls by tightening of the bolts 36 and a permanent bond is formed between transducers 18, 19 and 21 and the discs 22. This provides a columnar type of structure which is composed of rigid box-like sections able to support the driving frequency without internal deflection and, therefore, able to drive the resonant cavity 50 and the outside formation.

In operation, the motion of the inside mass 26 is built up until the spring reaction force drives the outside mass 23 with enough amplitude against the impressed load of the cavity-formation system to consume the applied power in sound power transmitted to the formation. Sound power is transferred to the surrounding formation by a combination of the RMS values of the factors of velocity of movement of the casing multiplied by the force of such movement. The sound power may be further described as the formation acoustic impedance times the total transducer plan area times the square of the casing RMS velocity or also as the product of the plan area times the sound RMS pressure squared divided by the acoustic impedance. This power or work rate must, of course, equal the electrical energy coupled into the system from the power source.

It has been observed that when the system comes into full operation with the masses vibrating at their normal amplitude and driving the resonant cavity at resonance, the applied current from the power source substantially comes into phase with the applied voltage thus indicating an eflicient transfer of electrical energy to the mechanical energy form which is in the form of sonic energy to the surrounding oil formation. As thus far described, it is believed that the energy distribution of the transducer element is best illustrated by a radiation pattern indicated by the lines 46 in FIG. 2 where the greatest density of the lines occurs along an axis which is in coincidence with the bolt 28 and piezoelectric element 27 In other Words, in a two-dimensional aspect the vibratory radiation from the transducer forms a major transmission pattern which is directed along a single axis essentially designated at 47 which is perpendicular to the vertical axis of the oil well. This, of course, means that it is also perpendicular to the axis of the casing 11.

The radiation field pattern 46 can be roughly analogized to the radiation pattern of a dipole antenna where the antenna has a double lobe energy distribution pattern illustrated in dashed lines at 48 and 49.

Since the force field of the present invention is similar to the dipole antenna, it is believed that certain precautions as to the design of the transducer with respect to the frequency used must be taken. It has been found that the circumferential distance around the outer periphery of mass 23 should be substantially equal to or greater than one wavelength in free liquid. If it is less than this, the sonic vibrations in one direction might tend to cancel those being produced on the other side of the transducer. For this reason, it is important to avoid too low a frequency since the effective gap between the two sides of the transducer along the axis 47 will have the appearance of a leak path and lower the efliciency of the transducer.

From yet another aspect, although a type of dipole radiation field is created, the medium itself, i.e., the oil bearing formation loss media, is not the same as that with a dipole antenna loss media. More specifically, the wavelength of sound in the medium, for example, oil, is the same order of magnitude as the flow path length of the oil. Thus, there may be preferred motion paths. Secondly, the medium is lossy from a sonic energy standpoint and thus the flow field has circulation and does not follow La Places Theorem. Lastly, there will be nor mally a considerable energy scattering effect since there are particles and discontinuities present in the medium.

A transducer assembly was constructed and tested. The transducer assembly comprised a cylindrical mass 23 made of leaded steel with a 5% inch O.D. having a 3%; inch diameter cylindrical cavity placed inch oif center. The cylindrical mass was 5% inches long. The cylindrical reaction mass 26 was made of leaded steel and was 3 /2 inches OD. and 4 inches long. The two piezoelectric transducers 27 were 2 /2 inch long tubes with 1 /2 inch OD. and inch I.D. They were made of PZT-8 material. They were mounted symmetrically on 2-inch centers in 1% inch O.D. holes and preloaded by inch bolts 28. The discs 22 were also made of leaded steel and were one inch thick with a 5 inch diameter corresponding to that of the mass 23. Four transducers were assembled and placed in a casing 11 having a 6% inch D. with a inch ID. The pump inlet 20 was approximately 30 feet above the transducer assembly to ensure liquid pressure about the transducer to eliminate cavitation.

With the foregoing assembly, 1000 watt alternating current power was applied. The assembly resonated at about 3750 cycles per second and the real electrical power input exceeded 1000 watts with a 900 volt RMS power supply driving the assembly.

The recovery rate from low gravity shallow oil wells has been substantially increased by using the transducer assembly of the present invention.

The double mass construction shown in a preferred embodiment of the invention provides eifective and efficient transfer of energy to the surrounding formation. It is believed that the improved electro-mechanical transducer is much more effective than prior types because it couples energy to a fluid medium with a specific type of radiation field.

What is claimed is:

1. An electro-mechanical transducer for coupling energy to a fluid medium comprising a transducer unit having a vibratory element having a longitudinal mode of vibration, electrical means for driving said vibratory element in said mode of vibration, a first mass interfacing with said fluid medium and having a predetermined geometrical axis and a cavity therein coaxial with said axis, a second mass having at least a portion extending into said cavity, and spring means including said vibratory element coupling said two masses with said longitudinal mode of said vibratory element perpendicular to the geometrical axis of said first mass so that the resulting spring forces are represented by a vector substantially perpendicular to said predetermined geometrical axis.

2. A transducer as in claim 1 which said two masses include air therebetween.

3. A transducer as in claim 1 which includes a plurality of said transducer units.

4. A transducer as in claim 1 which includes a plurality of sections each including at least one vibratory element, said sections being mechanically coupled to one another to form an elongated unitary transducer.

5. A transducer as in claim 4 wherein said sections are coupled to one another via a disc.

6. A transduced as in claim 5 in which bearing raceways are provided in each of said sections and in said disc and slightly oversized balls are provided in said raceways to form a permanent bond between said sections and the disc.

7. An electro-mechanical transducer adapted to be disposed in a well casing to couple energy to the fluid medium within said casing and formation surrounding said casing comprising a transducer unit having a vibratory element having a longitudinal mode of vibration, a first cylindrical mass interfacing with said fluid medium having a predetermined longitudinal axis and a cavity therein and adapted to fit within said well casing and having means supporting said mass in the well with the longitudinal axis thereof in a vertical portion, a second mass having at least a portion within said cavity, spring means including said vibratory element coupling said two masses with said longitudinal mode of said element perpendicular to the longitudinal axis of said first mass so that the resulting spring forces are represented by a vector substantially perpendicular to the longitudinal axis of said well casing, and means for driving said vibratory element at a frequency which has a wavelength substantially equal to the mean circumference of the space between the cylindrical element and the inside of the well casing.

8. A transducer as in claim 7 in which said two masses include air therebetween.

9. A transducer as in claim 7 which includes a plurality of said transducer units.

10. An oil well producing apparatus for increasing the production rate from oil producing formations in a production oil well comprising an electro-mechanical transducer means disposed in said well in the region of a producing formation, said transducer means having a major effective radiating surface providing energy radiation perpendicular to the axis of the well said radiation having a force pattern analogous to a dipole antenna with the major force being directed along a single axis perpendicular to the well axis and extending in opposite directions away from the well axis.

11. Apparatus as in claim 10 in which said transducer includes a two-mass spring system where first and second masses are coupled by a spring for providing said radiation. 7

12. Apparatus as in claim 11 in. which said spring has a major force vector substantially coincident with said single axis.

13. The method of increasing the production rate from an oil-producing formation in a production oil well having a cylindrical casing comprising the steps of disposing an electro-mechanical transducer in the region of the producing formation, causing said transducer to radiate energy in a dipole type radiation pattern having a single major eifective axis, and orienting said transducer so that said major effective axis is substantially perpendicular to the axis of said casing and extends in opposite directions away from said casing axis.

14. The method of increasing the production rate from an oil-producing formation in an oil well having a cylindrical casing comprising the steps of disposing an electromechanical transducer in the region of the producing formation, causing said transducer to radiate energy at a predetermined frequency into the cavity formed between the transducer and the well casing to cause the casing to move and to radiate energy into the surrounding forma- 8 tion substantially all of said radiated energy being radiated 2,670,801 3/ 1954 Sherborne 166-249 in a dipole type pattern perpendicular to the wells longi- 2,680,485 6/1954 Bodine 166-177 X tudinal axis, said predetermined frequency having a Wave- 3,287,692 11/1966 Turner 34010 length substantially equal to the mean circumference of 3,308,423 3/1967 Massa 3408 the cavity. 5 3,322,196 5/ 1967 Bodine 166--249 References Cited UNITED STATES PATENTS MARVIN A. CHAMPION, Primary Examiner Re 23381 6/1951 Bodine 166 249 I. A. CALVERT, Assistant Examiner 1,599,922 9/1926 Rathbone. m CL 2,184,809 12/1939 Brammer 166249 X 166 177; 34() 17 2,405,187 8/1946 Beniolf 340 1O 

